Otitis prone individuals have been identified as those having an episode of pneumococcal otitis media in the first year of life. IgE mediated reactions have been suggested as contributing to the pathogenesis of serous otitis media but mainly on the basis of classical atopic allergic manifestations. This investigation will determine the occurrence of IgE pneumococcal antibody in serums and middle ear fluids of infants with pneumococcal otitis media and the role that such antibody may play in the pathogenesis of this disease. We will determine what role the cell-mediated immune system may have in controlling these infections. In addition, we will determine what effects various treatment regimens have on both the immune response and frequency of recurrent episodes. Finally, this study will serve as a pilot field trial for determining the immune response of infants to vaccination with a polyvalent pneumococcal polysaccharide vaccine and if such a vaccination will be protective against certain serotypes of pneumococci causing otitis media. Humoral antibody will be qualitatively assayed by indirect immunofluorescence and quantitatively by radioimmunoassay. Antigens involved in an IgE reaction will be determined by radioimmunoassay and in vitro histamine release. The status of the cell-mediated immune system will be determined by thymidine uptake of stimulated lymphocytes in vitro and macrophage migration-inhibition factor in supernates from these cultures. Characterization of the role of the immune systems in this disease will serve as an important basis in our understanding the pathogenesis of a localized bacterial infection and determine optimal conditions for treatment and prevention.